The present invention relates to an automatic transmission for automobiles, and, more particularly, to an improvement of an automatic transmission for automobiles with regard to the control of its speed shift timing.
In an automatic transmission for automobiles including a gear means and a plurality of friction engaging means and adapted to establish various speed shift stages in accordance with selective engagement of said friction engaging means, if the timing of changing over the operation of the friction engaging means is not properly controlled, poor shift performance, such as to cause a shock to or a temporary revving-up of the engine, is caused. Conventionally, as a means for accomplishing smooth shifting in an automatic transmission for automobiles, it has been proposed to incorporate a one-way clutch in the transmission, and it is actually practiced to incorporate a one-way clutch in the shifting structure for changing over the lst and 2nd speed stages. However, if one-way clutches are incorporated in all the shifting structures for changing over various speed stages, the automatic transmission will become unduly big and expensive. Furthermore, since a one-way clutch idles in the reverse direction, it nullifies engine braking, thereby making it necessary to provide another means for effecting engine braking, thereby making the structure of an automatic transmission more complicated. Therefore, it is desirable that the timing for engaging and disengaging friction engaging means such as clutches and brakes is properly controlled without employing one-way clutches.